chore: use charmcraft 3

We can only currently build for one base, but we can remote build on launchpad
and thus get builds for all supported arches.

.github/workflows/ci.yml

@@ -36,7 +36,7 @@ jobs:
     needs: unit-tests
     uses: canonical/data-platform-workflows/.github/workflows/build_charms_with_cache.yaml@v4
     with:
-      charmcraft-snap-channel: 2.x/stable
+      charmcraft-snap-channel: 3.x/stable
       artifact-name: charm-packed
 
 
@@ -94,7 +94,7 @@ jobs:
         env:
           CHARMCRAFT_AUTH: ${{ secrets.CHARMCRAFT_AUTH }}
         run: |
-          sudo snap install charmcraft --channel 2.x/stable --classic
+          sudo snap install charmcraft --channel 3.x/stable --classic
           charmcraft upload ${{ steps.download.outputs.download-path }}/*.charm \
             --name $CHARM_NAME \
             --release ${{ needs.channel.outputs.test }}
@@ -180,7 +180,7 @@ jobs:
     steps:
     - name: Install Charmcraft
       run: |
-        sudo snap install charmcraft --channel 2.x/stable --classic
+        sudo snap install charmcraft --channel 3.x/stable --classic
 
     - name: Get uploaded revision
       id: revision

charmcraft.yaml

@@ -4,30 +4,9 @@ parts:
     charm-python-packages: [setuptools,markdown]
     build-packages:
       - cargo
-bases:
-    - build-on:
-        - name: ubuntu
-          channel: "22.04"
-          architectures: ["amd64"]
-      run-on:
-        - name: ubuntu
-          channel: "24.04"
-          architectures: 
-              - amd64
-              - arm64
-              - s390x
-              - ppc64el
-        - name: ubuntu
-          channel: "22.04"
-          architectures: 
-              - amd64
-              - arm64
-              - s390x
-              - ppc64el
-        - name: ubuntu
-          channel: "20.04"
-          architectures: 
-              - amd64
-              - arm64
-              - s390x
-              - ppc64el
+base: [email protected]
+platforms:
+  amd64:
+  arm64:
+  s390x:
+  ppc64el: